1. Field of the Invention
The field of the present invention is thin film ceramics. The present invention relates to the use of organometallic precursors and rapid thermal annealing for the synthesis of thin film ceramics.
2. Description of the Prior Art
Ceramic materials, and in particular ferroelectric ceramics have previously been prepared in a variety of ways that generally involve forming the ceramic ferroelectric body by pressing, casting, extrusion, or by means of thin sheet techniques, all followed thereafter by a burning or firing operation at elevated temperatures. The ceramic ferroelectric bodies are useful as capacitors, piezo-electric elements, transducers, and for various applications in the electrical field.
The majority of the prior art techniques result in a powder that is thereafter pressed or bonded into a usable form such as a pellet. Examples of such prior art include U.S. Pat. No. 4,019,915 (Miyauchi et al.), which discloses hot pressing and sintering under a high pressure, and U.S. Pat. No. 2,956,327 (Borel et al.), which discloses utilization of temperatures exceeding 900.degree. C. for extended periods of time combined with substantially elevated pressures resulting in a powder, paste, disc, or other shape of body. Other examples of prior art materials and methods are disclosed in U.S. Pat. No. 4,626,394 (Wada et al.), and U.S. Pat. No. 3,049,431 (Russell).
A particular class of useful ferroelectric ceramic materials are the perovskites, whose particular crystal structure allow them to be permanently electrically polarized. Such perovskites, which are the high temperature form for many mixed non-volatile memories, sensors, actuators, or non-linear optics due to their ability to produce a voltage when deformed. (For a general overview of ferroelectrics and perovskites, see Kirk-Othmer, Concise Encyclopedia of Chemical Technology, pp. 463-465 (1985).) At the present time, however, the usefulness of the perovskite materials has been limited by the inability to efficiently form thin film forms that can be used in today's microelectric devices. Therefore, the primary mechanism used today for non-volatile memories is the permanent magnetic bubble domain. This mechanism requires circuitry to drive it, thereby limiting its miniaturization capability and requires comparatively larger amounts of power for processing and use.
The prior art methods of producing ceramic materials, such as the ones previously discussed, are limited in their inability to form uniform, thin films. Most such prior art methods either involve high pressure and high temperature, both tending to add substantial cost to the processing of the ceramic, or they result in films that are overly thick or have excessive non-uniformity exhibited as pin holes. There is a need for thin film ferroelectrics, but ferroelectrics tend to lose their ferroelectric properties if they are originally made from bulk sources and only later attempted to be formed or used in thin sections or coatings.
In addition to the problems just discussed, in order to use such ceramic materials for silicon chips or other electronic components of this nature, a comparatively low processing temperature is required to avoid the melting or diffusion of the electronic circuitry and of the layered materials contained in the substrates. Furthermore, the thin film used in application to silicon chips must have good adhesion so that it will stick to the substrate without peeling or cracking. Adhesion can be the key in microelectronics where any possible locational variations can affect operation.
A still further problem in the manufacture of perovskite and other ferroelectric ceramics is meeting the product requirement of a substantially pure final material while still producing the requisite form or structure. Current methods of heating during the manufacturing of such ceramics typically heat the reacting materials at too slow a rate. This can result in the promotion of slow-forming products that are undesirable in addition to causing excessive diffusion within the substrate material.
Conversely, although there are a variety of current methods for making thin films such as sputtering, flow reacting, thermal evaporation, and chemical vapor deposition, their usefulness in manufacturing oxides or mixed oxide ceramics is limited due to the difficulty of dealing with the materials.
Accordingly, there exists a need for a rapid, efficient method of producing uniform thin films of ferroelectric or perovskite-type ceramics as well as other oxides.